In the production of specialty papers, there is substantial demand for the production of webs incorporating variegated coloring. Such webs have a wide variety of end uses, particularly but not necessarily in connection with the achievement of a decorative effect in the ultimate end product.
A variety of procedures have been developed in the past in an effort to produce a desirable quality of variegated paper web on an economical basis. In some instances, efforts have been made to introduce specially colored pulp into the paper making process, as for example was proposed in the Waite et al. U.S. Pat. No. 1,017,931. It has also been proposed to introduce coloring material onto the paper web as it is being formed on the Fourdrinier wire. The latter procedure, however, has not proven to be very successful in practice, as the color tends to contaminate the white water system such that, over time, color is more widely dispersed through the paper that is desired. The Carpenter U.S. Pat. No. 443,658 and Wildman et al. U.S. Pat. No. 1,827,923 are examples of the latter procedure.
The Feeney U.S. Pat. No. 1,964,567 illustrates a technique for the flowing of colorant onto the wet web at the couch roll. The procedure of the Feeney patent, however, is intended to provide a line configuration, and would have very limited ability to achieve a highly variegated design. Risk of contaminating the white water system is also present. The Crane U.S. Pat. No. 293,228 and Ellis et al. U.S. Pat. No. 330,215 reflect efforts to introduce color into the web between the wet press and dryer sections of the paper making line, but the procedures provide only for a highly regularized form of color application, in the nature of printing, which does not produce the desired, highly diffused, randomized coloring effect that is normally desired and sought for.
In accordance with the present invention, a novel and improved procedure and system is provided for the production of variegated paper, which provides for a high degree of control over the nature of the design and variegation and provides for an apparent randomized, highly diffuse pattern, without danger of contamination of the white water system. In accordance with the invention, variegated coloring is applied to a moving paper web at a nip station located downstream of the paper machine wire and, more specifically, between the wet press section and the dryer section, where the paper has an ideal moisture level for receptivity and diffusion of dye through the thickness of the web.
Pursuant to another aspect of the invention, the nip station, at which the variegated coloring effect is applied, includes a resilient transfer roller, located above the web and operative to apply pressure to the web as it traverses the nip. Dye is applied to the surface of the transfer roller, by means of a plurality of jet-like showers, spaced across the width of the transfer roller. Typically, there will be provided at least two such sets or arrays of jet-like showers, each typically discharging a dye of a different color, at each oscillating transversely with respect to the transfer roller. Ideal variegation is achieved by, among other things, oscillating the respective shower arrays at different frequencies and in a manner such that there is periodic overlapping of individual shower streams. The ultimate effect is the appearance of a high order of randomness to the design achieved and a particularly attractive and desirable end product.
In accordance with another and more specific aspect of the invention, a plurality of arrays of jet-like showers of dye solution are arranged above the transfer roller, directing jet-like streams of dye solution against the surface of the roller from a substantial distance. By controlling the pressure of discharge, and the angle at which the jet-like streams contact the transfer roller surface, a wide variety of design effects may be achieved which includes, where desired, a splashing effect, wide and/or narrow, variable-width wandering stripe-like areas, blotch-like areas and the like.
Among other things, the procedure according to the invention provides for the dye solutions to be "randomized" on the surface of the transfer roller and then pressed into the wet web at the roller nip, where further diffusion of the dye through the thickness of the wet web is achieved by reason of the optimum moisture content of the web at that juncture.
Pursuant to another aspect of the invention, a simplified, economical and reliable apparatus is provided for producing a variegated web on a continuous basis. The improved apparatus includes a nip station located between the wet press section and the dryer section of a paper machine and in which the upper roll of the nip station is a resilient transfer roller for the transfer of dyes in variegated patterns onto the still-wet web as it passes through the nip station. As the dye is transferred to the nip, it is thoroughly diffused through the web which, at that point in the paper making procedure is at an optimum moisture content for the purpose, and this diffusion process is aided significantly by the application of rolling pressure at the nip. The distribution of dye in variegated patterns is effected by providing, in conjunction with the transfer roller, a plurality, typically two, of transversely oscillating, multiple orifice dye shower arrays. These shower arrays are spaced a substantial distance from the transfer roller. Multiple jet-like streams of the dye liquid are issued from the multiple orifices, by means of appropriate supply systems, which maintain the dye under controllable pressure, usually different pressures in the individual arrays. Moreover, the shower arrays are mounted, usually adjustably, in such manner as to provide for the direction of the jet-like streams of dye onto the transfer roller surface at different angles, providing for both a variation in the length of travel of the jet-like streams in reaching the roller surface and also a difference in impact of the streams on the surface. The arrangement is such that, by controllable variation of stream pressure and angle of contact with the transfer roller, a wide variety of effects may be achieved, providing for an exceptionally desirable and attractive end product.
The invention is exceptionally useful in the production of specialty papers for use in the manufacture of simulated caning strips. Using web material produced according to the invention enables the end product to closely duplicate natural caning woods.